Internet Engineering Task Force (IETF) G. Nakibly
Request for Comments: 6324 NEWRSC
Category: Informational F. Templin
ISSN: 2070-1721 Boeing Research & Technology
August 2011
Routing Loop Attack Using IPv6 Automatic Tunnels:
Problem Statement and Proposed Mitigations
Abstract
This document is concerned with security vulnerabilities in IPv6-in-
IPv4 automatic tunnels. These vulnerabilities allow an attacker to
take advantage of inconsistencies between the IPv4 routing state and
the IPv6 routing state. The attack forms a routing loop that can be
abused as a vehicle for traffic amplification to facilitate denial-
of-service (DoS) attacks. The first aim of this document is to
inform on this attack and its root causes. The second aim is to
present some possible mitigation measures. It should be noted that
at the time of this writing there are no known reports of malicious
attacks exploiting these vulnerabilities. Nonetheless, these
vulnerabilities can be activated by accidental misconfiguration.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6324.
Nakibly & Templin Informational [Page 1]RFC 6324 Routing Loop Attack August 2011Copyright Notice
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Table of Contents
1. Introduction ....................................................2
2. A Detailed Description of the Attack ............................4
3. Proposed Mitigation Measures ....................................6
3.1. Verification of Endpoint Existence .........................6
3.1.1. Neighbor Cache Check ................................6
3.1.2. Known IPv4 Address Check ............................7
3.2. Operational Measures .......................................7
3.2.1. Avoiding a Shared IPv4 Link .........................7
3.2.2. A Single Border Router ..............................8
3.2.3. A Comprehensive List of Tunnel Routers ..............9
3.2.4. Avoidance of On-Link Prefixes .......................9
3.3. Destination and Source Address Checks .....................15
3.3.1. Known IPv6 Prefix Check ............................16
4. Recommendations ................................................17
5. Security Considerations ........................................17
6. Acknowledgments ................................................18
7. References .....................................................18
7.1. Normative References ......................................18
7.2. Informative References ....................................19
1. Introduction
IPv6-in-IPv4 tunnels are an essential part of many migration plans
for IPv6. They allow two IPv6 nodes to communicate over an IPv4-only
network. Automatic tunnels that assign IPv6 prefixes with stateless
address mapping properties (hereafter called "automatic tunnels") are
a category of tunnels in which a tunneled packet's egress IPv4
address is embedded within the destination IPv6 address of the
packet. An automatic tunnel's router is a router that respectively
encapsulates and decapsulates the IPv6 packets into and out of the
tunnel.